Table of Contents
- Introduction
- What is VMware vMotion?
- What is VMware Storage vMotion?
- VMware Enhanced vMotion Compatibility
- VMware vMotion without Shared Storage
- Thoughts
- Storage vMotion – A Brief Walkthrough
Introduction
One of the most interesting things about virtualized server resources is the flexibility it gives to move critical production workloads around between physical resources. Virtualization has allowed for abstracting the critical layers of server architecture away from the underlying host which affords tremendous mobility and agility to workloads running business-critical applications. Back in the legacy VMware days, most server administrators were hooked on virtualization after seeing this “magical” process called vMotion. The VMware vMotion technology allows seamlessly moving memory and CPU server workloads between hosts without any downtime or maintenance period to do so. Later VMware introduced what was called storage vMotion which allowed moving the underlying VMDK virtual disks to a new location while the virtual machine is running. Let’s dive deeper into vMotion and storage vMotion to see the similarities and differences in both technologies and what makes both possible. Also, we will look at enhanced vMotion as well as vMotion without shared storage.
What is VMware vMotion?
As mentioned, the VMware vMotion technology was responsible for many physical server administrators at the time getting excited about virtualization. The possibilities for maintenance and high availability were taken to new levels with the introduction of VMware vMotion. When vMotioning a virtual machine to another host, you are simply changing the host that is running the virtual machine. The associated virtual disk remains in the same location on storage that is shared between the two hosts. The really powerful part of the process of VMware vMotion is, the virtual machine is unaware of the change in the host it is running on. In fact, the move is transparent to the VM. Even the underlying networking is transferred such as the MAC address of the virtual machine.
Additionally, VMware vMotion is at the heart of the Distributed Resource Scheduler being able to successfully balance out resources. Virtual machines are moved between hosts in a vSphere cluster with DRS by using vMotion.
The VMware vMotion process is completed in three steps
- The virtual machine health is verified to be stable by vCenter Server
- The memory, registers, and network connections are copied to the target host (virtual machine state)
- The virtual machine is then able to resume operations on the new target host
There are a few considerations to be made in preparing the VMware ESXi host for vMotion. They include:
- CPU architecture is compatible between the source and target ESXi host
- Access to the datastores on which the virtual machine VMDKs are located
- If using VMware Standard vSwitches (VSS), virtual switches need to be labeled the same. This ensures network connectivity is maintained with the vMotion process for the virtual machine between hosts
- Making sure the virtual switch physical network connections and their respective network labels are consistent across the ESXi hosts
- VMware vMotion requires at least a gigabit network connection
- A vmkernel port must be enabled with the vMotion service
VMware has included some preemptive checks in the vMotion process to prevent a vMotion process from even being initiated if it detects a serious issue with the virtual machine and/or host configuration.
The vSphere ESXi host needs to have a vmkernel port configured with vMotion as an Enabled service
To perform a simple vMotion of a virtual machine on any given ESXi host, login to vCenter Server, right-click on a virtual machine and select Migrate. The migrate wizard will launch allowing you to select the type of migration to be performed.
When performing a simple vMotion – Change compute resource only is selected
What is VMware Storage vMotion?
Storage vMotion is a newer technology from VMware that allows migrating all virtual machine files from one storage location to another while the VM is powered on and without any downtime.
Storage vMotion completes the process of an entire virtual machine migration, not only allowing compute and memory to be transferred, but also allowing the disks to be moved as well.
As you can imagine, storage vMotion is extremely beneficial from a maintenance perspective. It allows VMware administrators to perform traditionally intrusive and disruptive storage maintenance without any virtual machine downtime, including VMFS upgrades. VMs can be moved from one storage device (while they are running) to the new storage location to allow maintenance to be performed.
Additionally, storage load or remaining capacity can be adjusted by moving virtual machine around as well using storage vMotion.
What are the requirements of storage vMotion? The following must be considered:
- VM disks must be persistent mode or RDMs
- If VMware Tools is in the process of installing on a virtual machine, the virtual machine cannot be storage vMotioned
- VMFS versions need to be considered. If moving from a newer version of VMFS to an older, the virtual disk sizes must be considered
- The host must be licensed for storage vMotion
- VMware vSphere hosts running ESXi 4.0 and later do not have to have vMotion configured to perform storage vMotion
Performing a storage vMotion using the Migrate wizard on a virtual machine
VMware Enhanced vMotion Compatibility
Starting in vSphere 5.1, VMware enabled the Enhanced vMotion Compatibility or EVC mode. The enhanced vMotion compatibility allows vMotion operations between dissimilar processors in ESXi hosts within the same cluster.
This allows migrating a virtual machine between a host with a certain micro architecture included with a CPU generation to a different CPU microarchitecture. For instance, using EVC mode, we can migrate a VM between a host running a Sandy Bridge processor and one with a Haswell processor.
At this point, you cannot migrate a running virtual machine between processors from different vendors such as Intel and AMD.
Enhanced vMotion is configured at the cluster level and disabled by default
Virtual machines that are powered off can be migrated between Intel and AMD processors by resetting the CPUID Mask settings however. But keep in mind, the virtual machine must be powered down to do this.
Changing CPUID Mask settings
VMware vMotion without Shared Storage
As part of the enhanced vMotion released with vSphere 5.1 and newer, vMotion no longer requires shared storage across hosts. This allows for cross-cluster migrations since the target hosts may not have access to the source datastores. The new functionality provides tremendous flexibility in how workloads are migrated and the requirements associated with the vMotion process.
Thoughts
Both vMotion and storage vMotion are powerful VMware technologies that allow migrating production workloads between hosts and storage.
This has allowed abstracting resources away from the underlying physical servers and enables allowing running virtual machines to move freely between hosts and even between clusters and dissimilar storage. This has allowed organizations tremendous flexibility in maintenance windows on the underlying hosts or storage systems. VMware vMotion is also at the heart of VMware DRS and other core technologies that distribute resources across clusters and allow making the most efficient use of available capacity.
VMware vMotion and storage vMotion provide a powerful mechanism to ensure flexibility, resiliency, agility, and mobility of virtual machine workloads.
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Storage vMotion – A Brief Walkthrough
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